Three-dimensional photography is comprehensively described in Three-Dimensional Imaging Techniques by Takanori Okoshi (New York: Academic Press, 1976, translated from the Japanese edition published in 1972) which provides a basis for describing the attributes and advantages of this invention. Okoshi initially distinguishes between truly three dimensional imaging and stereoscopic imaging on the basis of the amount of information involved. The quantity of information for a stereoscopic (or binocular) image is only twice that of a planar (one-dimensional) image, is much greater information is present for a truly three-dimensional image (which is often called an autostereoscopic image). Images of the latter type are truly spatial images that gradually show more of the right side of the object when the observer moves rightward, and more of the left side of the object when the observer moves leftward (which is often referred to as a "look around" capability). Integral photography is a method of recording a complete spatial image, that is, one viewable from a multiplicity of directions, upon a single flat photographic plate. The principles of integral photography were described by G. Lippman in 1908 in a paper read to the French Academy of Science. Integral photography thus has a long history of theoretical consideration and demonstration, but has enjoyed only limited commercial success.
Integral photography refers to the composition of the overall image as an integration of a large number of small photographic image components. Each photographic image component is viewed through a separate small lens usually formed as part of a mosiac of identical spherically-curved surfaces embossed or otherwise formed onto the front surface of a plastic sheet of appropriate thickness. The plastic sheet is subsequently bonded to or held in close contact with the emulsion layer containing the photographic image components. Lenticular photography is a special case of integral photography wherein the small lenses are formed as sections of cylinders running the full extent of the print area in the vertical direction. Recent commercial attempts at lenticular photography have included a multi-lensed 35 mm three-dimensional camera sold by Nimslo Corp., Atlanta, Ga., and a similar camera manufactured by Nishika Optical Systems, a division of Nishika Corp., Henderson, Nev. Though a sense of depth is clearly visible in prints made from these cameras, the resulting images have limited depth realism and appear to the viewer to "jump" as the print is rocked or the viewer's vantage relative to the print is changed.
The product of integral photography, that is, an integral photograph, can be further thought of as an X-Y array of microscopic slide projectors cascaded over the area of the print material. Each tiny lens, or lenslet, projects a microscopic view of the scene from a slightly different perspective than the one next to it. If the viewer's eye was concentrated on a singular lenslet surface, it would see only that portion of the view behind that lenslet which is angularly aligned with the line of sight to that lenslet. If the eye is moved laterally and continues to look at the same lenslet, it will see progressively different laterally angular portions of the view behind that lenslet. However, because the lenslets are made very small relative to the normal viewing distance, their apparent angular diameters may approach or subserve the angular resolution of the eye, with the result that features of the lenslets themselves are not apparent to the viewer, while the light emanating from them is.
The viewer then is able to mentally construct the entire array of optical beams from all lenslets into a recognizable scene without distraction from lenslet features. Since the right eye sees the array from a different vantage than the left eye, autostereoscopic depth perception is also present. By shifting the head laterally relative to the print surface, a changing autostereoscopic view is seen resulting in a "look around" capability which adds to the realism of the display. Integral photography also allows a "look around" capability in the vertical direction as well as the horizontal direction and an autostereoscopic view would also result if the print were rotated ninety degrees such that horizontal lines recorded from the original scene are now extending from bottom of the print to the top.
Since it is likely that most viewers prefer to view their photographs as models or reminders of the real world, it is not likely that they will choose to rotate the print for viewing. It was recognized as early as Lippman that instead of spherical lenslets, long cylindrical lenses extending from the top of the print to the bottom could be used to provide autostereoscopic views (and resultant "look around") in the horizontal direction only. This is sufficient to give a realistic three-dimensional model of the real world. Moreover, since vertical film space is not used to record alternative vertical views, the vertical detail recorded improves and approaches the film resolution limit, giving an improved impression of print quality. The long cylindrical lenses are called lenticules, and the principles of integral photography apply equally well to lenticular photography as long as one views the layouts or optical schematics in planes perpendicular to the cylindrical axis of the lenticules.
Since there are no restrains preventing any given lenticule from projecting information recorded behind adjacent lenticules and being seen by a viewer as the print is rotated about a vertical axis or when his head is moved laterally, the recorded sequence of perspective views will be repeated in viewer space. The maximum space for information to be printed behind a lenticule without extending into the recording space of an adjacent lenticule is the reciprocal of the lenticule pitch. The angle through which this information from a given lenticule is seen is called the primary angle. The images seen to each side of the primary angle are called satellite images. The pseudoscopic viewing occurs when one eye is within the primary image region (angle) and the other eye is in the satellite region (beyond the primary angle).
An optical method of making lenticular photographs is described by Okoshi in Chapter 4 of the aforementioned book.
It was determined through magazines such as Stereo World published by the National Stereoscopic association and from museums such as the Eastman House in Rochester N.Y., that sizable collections of stereoscopic photos of historical and societal interest exist unbeknownst to the general public. As such, these photos consist of only one stereo pair and are therefore not capable of reproducing the "look around" effect (which require many laterally separated views of a scene). The earliest patent describing this general technique of stereo pair recording is U.S. Pat. No. 1,128,979 issued to Hess on Feb. 16, 1915 and which describes the simplest optical system wherein the left L and right R views of a stereo pair are placed in plate holders held at angles symmetrical to a normal surface of a sheet of cylindrical lenses 100 (See FIG. 1). The cylindrical lens elements serve to focus sections of the images onto a photographic film 101. After development, the film was presumably carefully aligned and reaffixed to the cylindrical lens sheet for viewing. The image reversal induced by the lenticules in projecting the information is compensated by printing the Right view R to the left of the Left view L.
A principal problem with this type of image display is that the viewer is free to move laterally to a position beyond the primary angle where pseudoscopic viewing occurs thereby inverting the normal depth relationships as described earlier. This is illustrated in FIG. 2 where the left eye sees the Right image (R') aligned under the adjacent lenticule 102 and the right eye sees the Left image (L) under the reference lenticule 103.
By 1978, when the Nimslo camera was developed and marketed, four views of a scene were projected, comprising two left views and two right views. The inverse perspective pseudoscopic problem had still not been solved. This is illustrated in FIG. 3. As illustrated, four views are present under each lenticule: two Right views R.sub.1 -R.sub.2 (reference lenticule 105), R'.sub.1 -R'.sub.2 (adjacent lenticule 106) and two Left views L.sub.1 -L.sub.2 (reference lenticule 105), L'.sub.1 -L'.sub.2 (adjacent lenticule 106). An observer's eyes can move laterally relative to any given reference lenticule 105, for example as an arc 110 if the print is simply tilted in the viewer's hand. There are two positions A and B close to a normal to the print where correct perspective correlation viewing is possible. At position A, the right eye sees Right image R.sub.1 while the left eye sees Left image L.sub.2. At position B, the right eye sees Right image R.sub.2 while the left eye sees Left image L.sub.1. However, if the head moves further so that position C or D is reached, pseudoscopic viewing is experienced. In position C, the right eye sees Left image L.sub.1 while the left eye sees Right image R'.sub.2. In position D, the right eye sees Left image L.sub.2 while the left eye sees Right image R'.sub.1.
U.S. Pat. No. 4,800,407 describes an optical method of making three view parallax panoramograms. The three lens camera for 3D images described in this patent is still subject to the pseudoscopic image problem.
U.S. Pat. No. 4,852,972 introduces the concept of varying the exposure of views exposed by an optical method for the purpose of compensating for the transmission losses as the angle view increases.
U.S. Pat. No. 4,807,965 recognizes the pseudoscopic image problem and corrects it by preventing the observer from seeing pseudoscopic images by utilizing a mechanical system of Louvres, a constraint that would be expensive to implement and would act as an annoyance to consumers.
U.S. Pat. No. 4,959,641 also recognizes the pseudoscopic image problem and corrects it by independently controllable and discrete light sources provided in fixed relation to a lenticular screen. The problem of such a solution lies mainly in the complexity of the system.